This invention relates to security barriers. In particular, this invention relates to a security barrier that is effective when installed in soft ground.
Security barriers, or crash barriers, the main purpose of which being to prevent the passage of vehicles, are widely known in the art and have many applications. Common applications are for bordering dangerous sections of roads, providing a central separation between lanes of traffic moving in opposite directions, and around secure areas, for example around the entrance to airports or the like.
Known security barriers are generally made of metals, in particular steel, and comprise a post, which is bedded in concrete, and to which a barrier is attached. To provide the structural integrity to stop a car moving at around 40 to 50 km/h (about 25 to 30 mph), such barriers need a very deep, reinforced bedding of around a meter in depth and, for larger trucks, a bedding of up to two meters, into which the posts are set. As well as the obvious disadvantages in terms of the amount of material needed and the increased complexity of excavating to the required depth, the necessity of burying the posts to such a depth often interferes with existing buried services, for example electricity cables and sewage or water pipes. Although many are marked and can be anticipated during the planning stage, the discovery of pipes during deep excavation is common and necessitates halting excavation until the nature of the pipe/cable has been ascertained.
Typical designs of security fencing comprise a number of posts with tensioned steel cables between them. These fences typically run in lengths of in excess of a minimum of 50 meters, usually in excess of 100 meters. They generally comprise a very large end stop which will have a very large mass of concrete embedded in the ground, and against which the cables are tensioned. These systems have a number of problems associated with them. One of the problems is that if the fence is installed in uneven ground, i.e., if there is not a level line of sight between the two ends of the fence, between which the cables are tensioned, then tensioning the cable will place a load on each post, either pushing it into, or pulling it out of, the ground. A further problem is that due to the tensile nature of these fences, they may not be well suited for use in soft ground. This will increase the problem of the tensile forces acting on the posts which, if they are set in solid ground, may be acceptable to a degree. To date, so far as can be determined, none of these types of fences have managed to meet the stringent requirement of a PAS68 type test in soft ground.
It is the purpose of the present invention to provide an improved security barrier that at least partially mitigates the problems associated with the existing designs.